The invention relates to methods and apparatus for sealing an aperture More particularly, the present invention relates to methods and apparatus for sealing the aperture located between the first and second chambers of a dual chamber orifice fitting.
In pipeline operations and other industrial applications, flow meters are used to measure the volumetric flow rate of a gaseous or liquid flow stream moving through a piping section. Flow meters are available in many different forms. One type of flow meter is an orifice meter, which includes an orifice fitting connected to the piping section The orifice fitting serves to orient and support an orifice plate that extends across the piping section perpendicular to the direction of flow stream. The orifice plate is a thin plate that includes a circular opening, or orifice, that is positioned within the flow stream.
In operation, when the flow stream moving through the piping section reaches the orifice plate, the flow is forced through the orifice, thereby constricting the cross-sectional area of the flow. Due to the principles of continuity and conservation of energy, the velocity of the flow increases as the stream moves through the orifice. This velocity increase creates a pressure differential across the orifice plate The measured differential pressure across the orifice plate can be used to calculate the volumetric flow rate of the flow stream moving through the piping section.
A dual chamber orifice fitting enables the orifice plate to be removed from the fitting without interrupting the flow stream moving through the piping section. In many designs, this is achieved by providing two chambers within the fitting wherein the orifice plate is in the flow streams in one chamber and out of the flow stream in the second chamber An isolation valve is provided between the two chambers so as to prevent fluid communication between the two chambers when the valve is closed but also allow the orifice plate to pass between the chambers when the valve is open.
The isolation valves can be any of various devices that regulate the flow Of gases or liquids through the pipeline, piping or through related apertures by opening, closing, or obstructing ports or passageways. Many isolation valves comprise a stainless steel valve strip, or rectangular bar, which is manipulated by a valve carrier engaged with a drive mechanism such as a rack and pinion gear. The valve strip covers the aperture between the lower and second chambers and is biased against the aperture by springs and by the pressure of the fluid in the pipeline and first chamber.
In many instances, a chemical or petroleum based lubricant is injected between the valve strip and a seat surrounding the aperture. This lubricant acts to effectuate a seal along the interface between the valve strip and the seat. The performance of the seal is dependent on the dynamic viscosity of the lubricant If the fluid pressure differential across the seal exceeds the dynamic viscosity of the lubricant, the lubricant will shear and the seal will fail. Additionally, many lubricants are susceptible to degradation over time that can also result in leakage and failure of the seal.
Thus, the embodiments of the present invention are directed to apparatus and methods for sealing the aperture located between the first and second chambers of an orifice fitting that seek to overcome these and other limitations of the prior art.